Canine hearts are removed from donor dogs and perfused for 48 hours in a specially constructed chamber with a solution which is free of calcium and saline and rich in potassium, glucose, and oxygen. The perfusion pressure is constant at 18 mm. Hg. Coronary flow, fluid pH and electrolyte concentrations are monitored. At 48 hours of perfusion graft viability is tested by orthotopic homotransplantation into a suitable recipient.